I am having the exact same issue.  I upload an image, and after I "MoveTo" the image becomes locked.  I can't upload a file with the same name because I can't delete it with code.  I try to delete it manually with windows explorer, and it's locked by the IIS Worker Process as explained above. 

 

It works fine locally, it's just when I'm on the IIS 7  Windows 2008 server.  Is there something we can do to trouble shoot this?  This is very high priority for me.